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You are here: manpages

SNTP

Section: Programmer's Manual (1)
Updated: 2010-07-09
Index Return to Main Contents

NAME

sntp - standard SNTP program

SYNOPSIS

sntp [-flag [value]]... [--opt-name [[=| ]value]]...
hostname-or-IP ...

DESCRIPTION

This manual page briefly documents the sntp command. sntp can be used as a SNTP client to query a NTP or SNTP server and either display the time or set the local system's time (given suitable privilege). It can be run as an interactive command or in a cron job.

NTP (the Network Time Protocol) and SNTP (the Simple Network Time Protocol) are defined and described by draft-ietf-ntp-ntpv4-proto-13, which should become a full RFC any month now.

The default is to write the estimated correct local date and time (i.e. not UTC) to the standard output in a format like '1996 Oct 15 20:17:25.123 +4.567 +/- 0.089 secs', where the '+4.567 +/- 0.089 secs' indicates the local clock is 4.567 seconds behind the correct time (so 4.567 seconds must be added to the local clock to get it to be correct), and the time of is believed to be correct to within +/- 0.089 seconds.

OPTIONS

-4, --ipv4

Force IPv4 DNS name resolution. This option must not appear in combination with any of the following options: ipv6.

Force DNS resolution of following host names on the command line to the IPv4 namespace.

-6, --ipv6

Force IPv6 DNS name resolution. This option must not appear in combination with any of the following options: ipv4.

Force DNS resolution of following host names on the command line to the IPv6 namespace.

-d, --normalverbose

Normal verbose.

Diagnostic messages for non-fatal errors and a limited amount of tracing should be written to standard error. Fatal ones always produce a diagnostic. This option should be set when there is a suspected problem with the server, network or the source.

-K file-name, --kod=file-name

KoD history filename.

Modifies the filename to be used to persist the history of KoD responses received from servers. The default is /var/db/ntp-kod.

-p, --syslog

Logging with syslog. This option must not appear in combination with any of the following options: filelog.

When this option is set all logging will be done using syslog.

-l file-name, --filelog=file-name

Log to specified logfile. This option must not appear in combination with any of the following options: syslog.

This option causes the client to write log messages to the specified logfile.

-s, --settod

Set (step) the time with settimeofday(). This option must not appear in combination with any of the following options: adjtime.

-j, --adjtime

Set (slew) the time with adjtime(). This option must not appear in combination with any of the following options: settod.

-b broadcast-address, --broadcast=broadcast-address

Use broadcasts to the address specified for synchronisation.

If specified SNTP will listen to the specified broadcast address for NTP broadcasts. The default maximum wait time, 68 seconds, can be modified with -t.

-t seconds, --timeout=seconds

Specify the number of seconds to wait for broadcasts. This option takes an integer number as its argument. The default seconds for this option is:

68

When waiting for a broadcast packet SNTP will wait the number of seconds specified before giving up. Default 68 seconds.

-a auth-keynumber, --authentication=auth-keynumber

Enable authentication with the key auth-keynumber. This option takes an integer number as its argument.

This option enables authentication using the key specified in this option's argument. The argument of this option is the keyid, a number specified in the keyfile as this key's identifier. See the keyfile option (-k) for more details.

-k file-name, --keyfile=file-name

Specify a keyfile. SNTP will look in this file for the key specified with -a.

This option specifies the keyfile. SNTP will search for the key specified with -a keyno in this file. Key files follow the following format:

keyid keytype key

Where keyid is a number identifying this key
keytype is one of the follow: S Key in 64 Bit hexadecimal number as specified in in the DES specification. N Key in 64 Bit hexadecimal number as specified in the NTP standard. A Key in a 1-to-8 character ASCII string. M Key in a 1-to-8 character ASCII string using the MD5 authentication scheme.

For more information see ntp.keys(5).

-?, --help

Display extended usage information and exit.

-!, --more-help

Extended usage information passed thru pager.

-> [rcfile], --save-opts[=rcfile]

Save the option state to rcfile. The default is the last configuration file listed in the OPTION PRESETS section, below.

-< rcfile, --load-opts=rcfile, --no-load-opts

Load options from rcfile. The no-load-opts form will disable the loading of earlier RC/INI files. --no-load-opts is handled early, out of order.

- [{v|c|n}], --version[={v|c|n}]

Output version of program and exit. The default mode is `v', a simple version. The `c' mode will print copyright information and `n' will print the full copyright notice.

OPTION PRESETS

Any option that is not marked as not presettable may be preset by loading values from configuration ("RC" or ".INI") file(s) and values from environment variables named:

  SNTP_<option-name> or SNTP

The environmental presets take precedence (are processed later than) the configuration files. The homerc files are "$HOME", and ".". If any of these are directories, then the file .ntprc is searched for within those directories.

USAGE

The simplest use of this program is as an unprivileged command to check the current time and error in the local clock. For example:

: sntp ntpserver.somewhere

With suitable privilege, it can be run as a command or in a cron job to reset the local clock from a reliable server, like the ntpdate and rdate commands. For example: